1. Field of the Invention
The present invention relates to an adjustment device in a phase difference focus detection device used in single-reflex type cameras that detects the amount of focus deviation from the deviation of secondary images, and in particular, the invention relates to an adjustment device that causes the optical axis of the camera body and the optical axis of the focus detection unit in the phase difference focus detection device to coincide, in what is known as pupil adjustment.
2. Description of Related Art
A case wherein a phase difference focus detection block is incorporated into a single-reflex camera will be described hereafter with reference to FIG. 4.
A quick return mirror 20 having a half-reflective area in its center is positioned between the photographic lens 1 and the film plane 31. Light rays passing through the photographic lens 1 are reflected upward by the quick return mirror 20, these reflected light rays being directed to a viewfinder system comprised of a focussing plate 22, a condenser lens 23, a pentagonal prism 24 and an eyepiece lens 25. Light rays that pass through the half-reflective area of the quick return mirror 20 are reflected by a sub-mirror 21 and are directed to a focus detection block 11. The focus detection block 11 is comprised of a unit 10 to which a field of vision mask 2, a field lens 3, a diaphragm mask 4, reimaging lenses 5a1 and 5a2, a line sensor 6 and a reflecting mirror 7 are solidly fixed.
FIG. 5 is a diagram showing the structure of a standard phase difference focus detection optical system. The field of vision mask 2 is a device that restricts unnecessary light from outside the focus detection field of vision, the field lens 3 being comprised of a lens that places the pair of apertures 4a and 4b of the diaphragm mask 4 and the exit pupil of the photographic lens 1 in a conjugal relationship. The pair of reimaging lenses 5a1 and 5a2 are devices that re-image light rays passing through the various regions of the exit pupil of the photographic lens 1 on the line sensor 6, the line sensor 6 being comprised of a photosensitive element comprised of two components 6a1 and 6a2, which could, for example, be a CCD, which comprises a charge accumulation type photosensitive element. The mutual relationship between the positions of the two images formed by reimaging is found from an electrical signal from the photosensitive element comprised of the two components 6a1 and 6a2, from which the focus deviation amount of the photographic lens 1 can be calculated.
When the optical axis of the focussing block determined from the field of vision mask 2 through the reimaging lenses 5a1 and 5a2 does not coincide with the optical axis of the photographic lens 1 of the camera, the apertures 4a and 4b of the diaphragm mask 4 are not projected to the correct position on the exit pupil of the photographic lens 1 by the field lens 3. Because of this, an eclipse phenomenon occurs, wherein light rays that should enter the reimaging lenses 5a1 and 5a2 are blocked by the exit pupil of the photographic lens, having a negative effect on the precision of focus detection.
Therefore, adjustment known as pupil adjustment is necessary, wherein the optical axis of the photographic lens 1 of the camera and the optical axis of the focussing block from the field of vision mask 2 through the reimaging lenses 5a1 and 5a2 are made to coincide. Specifically, pupil adjustment consists of the focus detection block 11 being mounted on the camera body using three screws and springs so that the optical axis can be adjusted by changing the inclination of the entire focus detection block 11 by turning the screws. It is also possible to move the field lens 3 in a plane perpendicular to the optical axis of the lens, as is set forth in Japanese Laid Open Patent Application No. 62-161111 (page 3, from line 15 of the upper right column through line 6 of the lower left column).
A device in which focus detection is performed on a plurality of areas on the screen in a focus detection device used in a camera is set forth in Japanese Laid Open Patent Application No. 63-11906 (FIG. 1 and line 12 of the upper right column of page 2 through line 3 of the second left column of page 3).
FIG. 6 presents an example where focus detection is performed on the three areas shown therein, in which the basic structure of the optical system does not differ from that of FIG. 4.
Light rays passing through the half-reflective area of the quick return mirror 20 are reflected by the sub-mirror 21 and directed to the focus detection block 90, the focus detection block 90 being comprised of a field of vision mask 12, a field lens 13, a diaphragm mask 14, a reimaging lens 15, a line sensor 16 and a mirror 7. These structures are fixed to a unit formed of synthetic resin or similar material (not shown in the drawing).
The field of vision mask 12 has three apertures 12a, 12b and 12c. In FIG. 6, the center aperture 12a of the field of vision mask 12 is horizontal, while the other two apertures 12b and 12c are vertical. The field lens 13 has three lens units 13a, 13b and 13c formed as a single entity. The diaphragm mask 14 also has three pairs of diaphragm apertures, as indicated by the dashed lines.
The reimaging lens 15 has three pairs of reimaging lens components 15a1 and 15a2, 15b1 and 15b2, and 15c1 and 15c2, and the line sensor 16 includes three pairs of light receptors 16a1 and 16a2, 16b1 and 16b2, and 16c1 and 16c2 corresponding to the three areas. The field of vision mask 12a, 12b and 12c, the field lens 13a, 13b and 13c, the diaphragm mask 14a, 14b and 14c, the reimaging lens 15a, 15b and 15c and the line sensor 16a, 16b and 16c comprise independent optical systems that perform focus detection in each of the three areas.
However, in adjusting the above-described focus detection block 90, which performs focus detection in three areas, when pupil adjustment is performed for one area by attaching the focus detection block 90 to the camera body using screws and springs and changing the inclination of the focus detection block 90 as a whole by turning the screws, independent adjustment of the other two areas cannot be performed.
In addition, even when the field lens 13 is moved in a plane perpendicular to its optical axis, as set forth in Japanese Laid Open Patent Application No. 62-161111, when the field lenses corresponding to each area are formed as a single entity as in Japanese Laid Open Patent Application No. 63-11906, adjustment can be performed on only one area.